Sorry but Doug is wrong on the TR4 but right on the TR6. The TR4/4A rear studs screw in and are peened over on the back to hold them in. The front studs (only) are knurled and can be knocked out and replaced on the TR4, but on the TR6 F&R are the same process.
If yout TR4 rear stud spins, we will need more information as to the condition of the hub for a recommendation on how to proceed with the repair. Remove the wheel as martx-5 suggested and report back please. If the threads are totally gone, you may be able to drill out to fit a standard sized press-in/draw-in stud (Chevy) to replace it.